I. Field of the Invention
This invention relates generally to the design of a hydraulic motor and more specifically to a Gerotor hydraulic motor in which provision is made for controlling the pressure exerted on the shaft and shaft seals as well as upon the rotor element of the Gerotor assembly.
II. Description of the Prior Art
Gerotor hydraulic motors, per se, are well known in the art. In this arrangement an inner gear is keyed to, and rotates with, the shaft to be driven. An outer gear of the internal type is driven by the hydraulic fluid introduced through timing crescents formed in the adjacent end and front plates and is free to rotate with a snug fit in a stator which forms a part of the housing. The inner gear has a lesser number of teeth than is provided in the outer gear and the teeth of the two gears are specially shaped so that the top of all teeth of the inner gear are always in sliding contact with the teeth of the outer gear.
In accordance with the present invention, the Gerotor elements are sandwiched between an end plate and a front plate and one end of the shaft is journaled for rotation in the end plate while the other end of the shaft is journaled in suitable bearings in the front plate. A shaft seal is disposed in the front plate in proximity to the front plate bearings to prevent the leakage of hydraulic fluid along the shaft and past the front shaft bearings.
Hydraulic fluid, under high pressure, for example, 2,000 PSI may be made to selectively flow through a first or a second port formed in the endplate which communicates with the crescents abutting the Gerotor elements. The remaining port communicates with the low pressure side of the Gerotor element. In known prior art arrangements, motors of the Gerotor type are only designed to produce unidirectional shaft rotation, either clockwise or counter clockwise, but not both. The motor design of the present invention, however, allows a reversal in the direction of rotation by simply controlling the flow of the high pressure hydraulic fluid to the inlet/outlet ports, while still providing pressure relief to the shaft seal. Also, to accommodate bidirectional rotation of the shaft, first and second motoring grooves are provided between the stator element of the Gerotor and the internal toothed outer gear. These motoring grooves cooperate with motoring groove feed channels formed in the motor front plate and with corresponding shadow feed channels formed in the end plate. As such, axial thrust forces which would otherwise exist on the faces of the inner and outer gear elements of the Gerotor assembly are balanced, irrespective of the direction of rotation of the outer gear with respect to the stator.
Also in the preferred embodiment of the present invention, means are provided to relieve the high pressure which would exist on the end of the motor shaft tending to displace it outwardly if this relief structure were not provided.
The Banker U.S. Pat. No. 3,433,168 discloses the use of a pressure relief valve in combination with a gear-type pump such that if the output pressure of the pump is too great, the pressure relief valve will open to permit fluid into the input port. This patent does not disclose the feature of the present invention wherein first and second ball-check type pressure relief valves are disposed in relationship to the bearing end seal to provide pressure relief thereto irrespective of the direction of rotation of the motor shaft. Similarly, the Compton U.S. Pat. No. 3,289,601 discloses in FIG. 7 thereof a Gerotor-type motor/pump having a channel 165 communicating with an annular recess 166 formed in the front plate. This arrangement is designed to provide pressure relief to the bearing seal 118, but it is to be noted that in the Compton patent, such pressure relief only occurs when the high pressure side of the hydraulic system is connected to the input port 49 and the low pressure connection is made to the output port 40. If an attempt were made to reverse the direction of rotation of the motor by interchanging the input/output port connections, no such relief would be available. Similarly, the Compton patent does not include a pressure relief valve in communication with the annular recess 166.